STRENGTH AND DEFORMATION BEHAVIOUR OF DAM FOUNDATION ON JOINTED ROCK MASS

Abstract

Dams have been a vital part of human civilization. History has amply documented close association of dams with the rise and fall of civilizations, especially those highly dependent on irrigation. High dams, impounding large volumes of water, have been and continue to be constructed on the rivers around the world for hydro-electric power generation, flood control, irrigation, water supply, navigation, recreation and other purposes. The benefit of dams to mankind is unquestionable. Their earliest role was to provide storage of water for irrigation which was vital for agriculture production in many countries. Then, the role expanded to providing water for transport, industrial processes, and the growing cities. In the 18th century, dams were constructed to store water for canals; during 19th century, the majority of dams were built for water supply as well; and early in the 20th century, they were constructed for hydropower generation as well. A dam is a hydraulic structure constructed across a river to store water on its up-stream side. It is an impervious or fairly impervious barrier put across a natural stream so that a reservoir is formed. This water is then utilized as and when it is needed. Due to the construction of the dam, water level in the river at its up-stream side is very much increased, and a large area may be submerged depending upon the water spread of the reservoir so formed. A gravity dam is a structure so proportioned that its own weight resists the forces exerted upon it. This type of dam is the most permanent one, requires little maintenance and is most commonly used. An arch dam is a dam curved in plan and carries a major part of its water load horizontally to the abutments by arch action. The part of the water load depends primarily upon the amount of curvature. The balance of the water load is transferred to the foundation by cantilever action. An arch-cum-gravity dam is a dam consisting of both the properties of an arch dam as well as gravity dam. Its structure is so proportioned that its self weight and arch action resists the forces exerted upon the dam. A 192.0 m high straight concrete gravity dam has been proposed at Lakhwar across river Yamuna in Distt. Dehradun of uttarakhand. The dam foundation is very complex and consists of quartzitic slates, trapes, thinly foliated slates and a 1.5 m thick shear zone exists about 70 m below the toe of the dam and traverses into the left abutment. iii A 3-D FEM analysis for straight concrete gravity dam showed a horizontal deflection of 4.4 cm at the top and vertical deflection of 7.35 cm at the toe of the dam. Alternatively, an arch cum gravity concrete dam has been proposed. The present analysis of arch cum gravity dam shows that horizontal deflection at top has now reduced to 3.94 cm. The maximum vertical deflection at toe is 7.08 cm. The study shows that deflections are within reasonable limits. A suitable layout along with the treatment of left blank will attribute to the suitability of arch cum gravity dam at Lakhwar. iv